The two factions have been at each others’ throats for years, most recently because of al-Qaeda’s role as a major rebel faction in Syria, and Hezbollah’s alliance with the Assad government.

The two sides are both claiming major losses on the opposing side, though exact death tolls are unclear. Hezbollah admitted to nine deaths on their side, including three in an ambush Wednesday when they tried to move into a Shi’ite town in Syria. Lebanese officials put the Nusra toll at 26 fighters killed this week.

Nusra and other rebel factions have long tried to use the Lebanese border reason as a staging ground, while Hezbollah has been trying to chase the rebels out of Syrian towns, particularly the Shi’ite towns along the border that have large amounts of Lebanese residents.